//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Linq;

namespace Microsoft.Practices.Prism.Events
{
	/// <summary>
	/// Defines a class that manages publication and subscription to events.
	/// </summary>
	/// <typeparam name="TPayload">The type of message that will be passed to the subscribers.</typeparam>
	public class CompositePresentationEvent<TPayload> : EventBase
	{
		private IDispatcherFacade uiDispatcher;

		/// <summary>
		/// Gets the <see cref="Dispatcher"/> that is bound to the UI elements.
		/// </summary>
		/// <value>The <see cref="Dispatcher"/> to use when subscribing using <see cref="ThreadOption.UIThread"/>.</value>
		private IDispatcherFacade UIDispatcher
		{
			get
			{
				if (uiDispatcher == null)
				{
					this.uiDispatcher = new DefaultDispatcher();
				}

				return uiDispatcher;
			}
		}

		/// <summary>
		/// Subscribes a delegate to an event that will be published on the <see cref="ThreadOption.PublisherThread"/>.
		/// <see cref="CompositePresentationEvent{TPayload}"/> will maintain a <seealso cref="WeakReference"/> to the target of the supplied <paramref name="action"/> delegate.
		/// </summary>
		/// <param name="action">The delegate that gets executed when the event is published.</param>
		/// <returns>A <see cref="SubscriptionToken"/> that uniquely identifies the added subscription.</returns>
		/// <remarks>
		/// The CompositePresentationEvent collection is thread-safe.
		/// </remarks>
		public SubscriptionToken Subscribe(Action<TPayload> action)
		{
			return Subscribe(action, ThreadOption.PublisherThread);
		}

		/// <summary>
		/// Subscribes a delegate to an event.
		/// CompositePresentationEvent will maintain a <seealso cref="WeakReference"/> to the Target of the supplied <paramref name="action"/> delegate.
		/// </summary>
		/// <param name="action">The delegate that gets executed when the event is raised.</param>
		/// <param name="threadOption">Specifies on which thread to receive the delegate callback.</param>
		/// <returns>A <see cref="SubscriptionToken"/> that uniquely identifies the added subscription.</returns>
		/// <remarks>
		/// The CompositePresentationEvent collection is thread-safe.
		/// </remarks>
		public SubscriptionToken Subscribe(Action<TPayload> action, ThreadOption threadOption)
		{
			return Subscribe(action, threadOption, false);
		}

		/// <summary>
		/// Subscribes a delegate to an event that will be published on the <see cref="ThreadOption.PublisherThread"/>.
		/// </summary>
		/// <param name="action">The delegate that gets executed when the event is published.</param>
		/// <param name="keepSubscriberReferenceAlive">When <see langword="true"/>, the <seealso cref="CompositePresentationEvent{TPayload}"/> keeps a reference to the subscriber so it does not get garbage collected.</param>
		/// <returns>A <see cref="SubscriptionToken"/> that uniquely identifies the added subscription.</returns>
		/// <remarks>
		/// If <paramref name="keepSubscriberReferenceAlive"/> is set to <see langword="false" />, <see cref="CompositePresentationEvent{TPayload}"/> will maintain a <seealso cref="WeakReference"/> to the Target of the supplied <paramref name="action"/> delegate.
		/// If not using a WeakReference (<paramref name="keepSubscriberReferenceAlive"/> is <see langword="true" />), the user must explicitly call Unsubscribe for the event when disposing the subscriber in order to avoid memory leaks or unexepcted behavior.
		/// <para/>
		/// The CompositePresentationEvent collection is thread-safe.
		/// </remarks>
		public SubscriptionToken Subscribe(Action<TPayload> action, bool keepSubscriberReferenceAlive)
		{
			return Subscribe(action, ThreadOption.PublisherThread, keepSubscriberReferenceAlive);
		}

		/// <summary>
		/// Subscribes a delegate to an event.
		/// </summary>
		/// <param name="action">The delegate that gets executed when the event is published.</param>
		/// <param name="threadOption">Specifies on which thread to receive the delegate callback.</param>
		/// <param name="keepSubscriberReferenceAlive">When <see langword="true"/>, the <seealso cref="CompositePresentationEvent{TPayload}"/> keeps a reference to the subscriber so it does not get garbage collected.</param>
		/// <returns>A <see cref="SubscriptionToken"/> that uniquely identifies the added subscription.</returns>
		/// <remarks>
		/// If <paramref name="keepSubscriberReferenceAlive"/> is set to <see langword="false" />, <see cref="CompositePresentationEvent{TPayload}"/> will maintain a <seealso cref="WeakReference"/> to the Target of the supplied <paramref name="action"/> delegate.
		/// If not using a WeakReference (<paramref name="keepSubscriberReferenceAlive"/> is <see langword="true" />), the user must explicitly call Unsubscribe for the event when disposing the subscriber in order to avoid memory leaks or unexepcted behavior.
		/// <para/>
		/// The CompositePresentationEvent collection is thread-safe.
		/// </remarks>
		public SubscriptionToken Subscribe(Action<TPayload> action, ThreadOption threadOption, bool keepSubscriberReferenceAlive)
		{
			return Subscribe(action, threadOption, keepSubscriberReferenceAlive, null);
		}

		/// <summary>
		/// Subscribes a delegate to an event.
		/// </summary>
		/// <param name="action">The delegate that gets executed when the event is published.</param>
		/// <param name="threadOption">Specifies on which thread to receive the delegate callback.</param>
		/// <param name="keepSubscriberReferenceAlive">When <see langword="true"/>, the <seealso cref="CompositePresentationEvent{TPayload}"/> keeps a reference to the subscriber so it does not get garbage collected.</param>
		/// <param name="filter">Filter to evaluate if the subscriber should receive the event.</param>
		/// <returns>A <see cref="SubscriptionToken"/> that uniquely identifies the added subscription.</returns>
		/// <remarks>
		/// If <paramref name="keepSubscriberReferenceAlive"/> is set to <see langword="false" />, <see cref="CompositePresentationEvent{TPayload}"/> will maintain a <seealso cref="WeakReference"/> to the Target of the supplied <paramref name="action"/> delegate.
		/// If not using a WeakReference (<paramref name="keepSubscriberReferenceAlive"/> is <see langword="true" />), the user must explicitly call Unsubscribe for the event when disposing the subscriber in order to avoid memory leaks or unexepcted behavior.
		/// 
		/// The CompositePresentationEvent collection is thread-safe.
		/// </remarks>
		public virtual SubscriptionToken Subscribe(Action<TPayload> action, ThreadOption threadOption, bool keepSubscriberReferenceAlive, Predicate<TPayload> filter)
		{
			IDelegateReference actionReference = new DelegateReference(action, keepSubscriberReferenceAlive);
			IDelegateReference filterReference;
			if (filter != null)
			{
				filterReference = new DelegateReference(filter, keepSubscriberReferenceAlive);
			}
			else
			{
				filterReference = new DelegateReference(new Predicate<TPayload>(delegate { return true; }), true);
			}
			EventSubscription<TPayload> subscription;
			switch (threadOption)
			{
				case ThreadOption.PublisherThread:
					subscription = new EventSubscription<TPayload>(actionReference, filterReference);
					break;
				case ThreadOption.BackgroundThread:
					subscription = new BackgroundEventSubscription<TPayload>(actionReference, filterReference);
					break;
				case ThreadOption.UIThread:
					subscription = new DispatcherEventSubscription<TPayload>(actionReference, filterReference, UIDispatcher);
					break;
				default:
					subscription = new EventSubscription<TPayload>(actionReference, filterReference);
					break;
			}


			return base.InternalSubscribe(subscription);
		}

		/// <summary>
		/// Publishes the <see cref="CompositePresentationEvent{TPayload}"/>.
		/// </summary>
		/// <param name="payload">Message to pass to the subscribers.</param>
		public virtual void Publish(TPayload payload)
		{
			base.InternalPublish(payload);
		}

		/// <summary>
		/// Removes the first subscriber matching <seealso cref="Action{TPayload}"/> from the subscribers' list.
		/// </summary>
		/// <param name="subscriber">The <see cref="Action{TPayload}"/> used when subscribing to the event.</param>
		public virtual void Unsubscribe(Action<TPayload> subscriber)
		{
			lock (Subscriptions)
			{
				IEventSubscription eventSubscription = Subscriptions.Cast<EventSubscription<TPayload>>().FirstOrDefault(evt => evt.Action == subscriber);
				if (eventSubscription != null)
				{
					Subscriptions.Remove(eventSubscription);
				}
			}
		}

		/// <summary>
		/// Returns <see langword="true"/> if there is a subscriber matching <seealso cref="Action{TPayload}"/>.
		/// </summary>
		/// <param name="subscriber">The <see cref="Action{TPayload}"/> used when subscribing to the event.</param>
		/// <returns><see langword="true"/> if there is an <seealso cref="Action{TPayload}"/> that matches; otherwise <see langword="false"/>.</returns>
		public virtual bool Contains(Action<TPayload> subscriber)
		{
			IEventSubscription eventSubscription;
			lock (Subscriptions)
			{
				eventSubscription = Subscriptions.Cast<EventSubscription<TPayload>>().FirstOrDefault(evt => evt.Action == subscriber);
			}
			return eventSubscription != null;
		}

	}
}